Extending the length of a vario antenna

[flyboy320]

I have a glider that has a carbon fiber fuselage and would like to extend the antenna of my vario out through the tail (for space reasons the vario has to be mounted up front). For me to do this, I would have to extend the length of the current antenna (to about 52 inches) . Can this be safely done without damaging the transmitter in the vario?

I got the idea from extending the 31mm length of my AR9000 rx antenna to 62mm so I could extend 31mm of it outside the fuse (since the cf fuse blocks the rx unless its placed outside the fuse).

I would solder a wire onto the end of the existing one to make an antenna length a multiple of half a wavelength of 433 mhz (which is the frequency the tx in the vario transmits on) to 12.97", using the web page here to calculate to required length;

http://www.crompton.com/wa3dsp/hamradio/antcalc.html

I tried using the vario with the antenna inside the fuse, but I could not receive the vario much past 50 feet.

I just would like to know if this extra antenna length can cause the transmitter any problems (can it overload the tx, or does extending the length of an antenna have nothing to do with taking power form the transmitter)?

[Ron W3FJW]

You should probably use a small coax from the Tx to the tail and then attach a 6.5" (1/4 wave) piece of wire to the center conductor for outside of the fuselage. Connect the shield to the Tx ground.
How far is it from the Tx to the tail? The coax should be a multiple of a half wave long.

[Tomapowa]

...

[flyboy320]

You should probably use a small coax from the Tx to the tail and then attach a 6.5" (1/4 wave) piece of wire to the center conductor for outside of the fuselage. Connect the shield to the Tx ground.
How far is it from the Tx to the tail? The coax should be a multiple of a half wave long.

The distance is about 40" from where the vario will be mounted (beneath the wing) and the exit hole in the tail. The vario already has a 13" (or there abouts) antenna on it, and it the way the vario is designed, it would be hard to remove the antenna from the tx in the vario without cutting it, which I would want to avoid if at all possible (I don't think the circuit board is accesable). So with that in mind, could I attach the coax to the end of the installed antenna, and then run it to the tail (using a length of a multiple of a half wavelength), and attach a 6.5" wire to the end, so in effect I would have the vario antenna, coax, and then another antenna?

Actually, come to think on it, I have some RG174U coax that I got for shielding the rx antenna on my AR9000 (wi-fi coax). Would this work for a tx transmitting on 433mhz?

[JPMacG]

If you make the RG174 1/4 wavelength long and allow the center conductor to extend beyond the end of the braid by 1/4 wavelength you will have a sleeve dipole. This should work well. Of course, the braid of the RG174 becomes essentially one side of a dipole.

On second thought, this is a bad idea. Never mind.

[Ron W3FJW]

Unfortunately, the coax would need to be soldered on the Tx board otherwise you'll just have a long piece of wire.
I don't know what your use is, but one option would be to mount the Tx on the bottom of the fuse and extend the antenna out the bottom.
Another option (maybe) would be to ground your batt - to the carbon fiber, run a piece of wire out the tail and hope the fuselage might act like the outer braid.
Do you have a link to the Vario? Or some specs?

[flyboy320]

Well I just made a wire extension and soldered it to the original antenna so the total length of the new antenna is 51.88" (4x12.97") and ran this to the tail, and have 12.97" sticking out the back of the cf fuse. I'm hoping by keeping the total length of the antenna to a multiple of 1/2 wavelength (12.97"), and in addition having 1/2 wavelength antenna out the back free of the cf fuse (12.97") that this will give me good reception.

I'll have to wait till some good weather now as its raining and windy for the next few days...:cool:

The vario is a Wstech;

http://www.wstech.de/english/index_e.htm

And the manual;

http://www.wstech.de/english/Vario_Voice_Bedien_engl.pdf

If this doesn't work, the last resort is to do what you suggest Ron, and drill a hole in the fuse and run the antenna out that way. I just want to avoid doing that if at all possible, but not the end of the world if that's what has to be done.

[flyboy320]

Just came back from testing. I had it up to 500' and the vario was loud and clear. The antenna mod seems to work very well. Before I could only get reception from less than 50' away, so all is good... :)

Thanks for eveyones help....